Hollow building blocks, generally cast of concrete, are commonly used to erect longitudinal vertically stacked arrays of like blocks to form building walls and interior partitions. A bead of mortar is placed along the interior and exterior upper edges of a base course of blocks, and along the interior and exterior side edges of the placed block to join the stacked array of blocks together. Before the mortar sets or hardens, the outer surface of the mortar bead between the stacked blocks is tooled. Tooling involves compacting, shaping and smoothing the outer mortar surface with a generally semi-circular shaped tool to ensure that no voids or cracks remain in the mortar joint which would allow moisture penetration, and to give the desired finished joint appearance.
Infiltration of water through cracks in the mortar or block, and migration of water through the hollow block from the exterior of a building to the interior is a major problem. Ground water may pass through basement walls and rain water may pass through other walls resulting in damage to the building structure and contents. A variety of causes account for water penetration of block walls including: wall settlement; improper mortar compaction or composition; voids in mortar or block; and inherent permeability of the mortar and block material.
Basement walls are often made of cast-in-place concrete. Concrete and block basement walls are coated on their exterior with waterproofing coatings such as tar to prevent leakage of ground water. Above ground cavity walls are constructed comprising an exterior brick layer and an interior block layer defining a cavity and the layers being connected with metal ties. Cavity walls have metal flashing and weep holes at their base to expel water above the ground level. Since cavity walls are really two separate walls tied together, the costs involved are relatively high compared to a single thickness block wall. Transparent chemical coatings have also been applied to the exterior of masonry walls to seal them, however, the service life of such coatings is limited and coatings must be reapplied periodically to preserve the seal.
A preferred method of constructing a masonry wall generally includes a single layer of concrete blocks since the above alternatives are relatively expensive, and modern concrete block designs may include colours, textures and surface features having all the aesthetic appeal of brick at a lower cost. Concrete block walls are of relatively low cost due to manufacturing and handling advantages and the skill involved in laying a block wall is less exacting than many other construction methods.
A conventional hollow building block especially in North America comprises interior and exterior parallel vertical walls with three transverse vertical webs spanning between the walls to form a rigid unitary block usually cast of concrete within a mould. The webs are inset from the transverse sides of the block such that the walls and web define two cavities within the block and, when like blocks are assembled into a constructed building wall, a cavity is defined between the outer transverse webs of adjacent blocks. The interior dimensions of the individual cavities of a block are slightly tapered to facilitate stripping of the mould from the block. Therefore, when overlapped blocks are vertically stacked, a vertical series of cavities results. Conventional metal flashing and weep holes at the ground level of the wall direct any water from within the vertical cavities outward.
Accordingly, there is a need for water controlling hollow building block which can be stacked in a single course to form a building wall. United Kingdom Patent No. 611,285 to Thomas Harvey 27 Oct. 1948 describes a hollow building block having longitudinal grooves in its upper and lower surfaces to impede the infiltration of water between the block and mortar joint and, to redirect the water to flow downwardly through cavities in the block. United Kingdom Patent No. 778,527 to John O'Connell 10 Jul. 1957 describes an improved hollow concrete block having three rows of cavities providing for one or more cavities in any vertical transverse cross section to prevent water migration through the inherently permeable material of the block. O'Connell also includes a groove in the upper surface of a block web to impede water flow.
Such proposed hollow block designs do not address the problem of water migrating from the exterior of the block to the interior by trickling down the side surfaces of transverse webs of vertically stacked blocks. Water will not trickle in a strictly vertical path down the side surface of the web but will form rivulets which run laterally and downwardly across the rough web surface in a random fashion. Since a mortar bead is placed only on the interior and exterior upper edges of a block, a gap is located in the central region of the web between the parallel mortar beads. Water flowing down the web of a block upon encountering the gap between blocks drips into the cavity of the block below. As a result, water may migrate across the webs of such proposed hollow blocks. The water may eventually pass from a crack in the exterior of the block wall to the interior of the block wall through a crack in the interior of the block wall or water may be absorbed by the interior mortar bead and bleed through to the interior of the building.